This invention relates to treatment of wastewater containing citric acid and/or triethanolamine generated from ship bilge cleaning operations, for disposal thereof, and is particularly concerned with the destruction and decomposition of the citric acid and triethanolamine in such wastewater.
One of the regular maintenance tasks for surface ships is ship bilge cleaning. For this purpose, solutions containing citric acid and triethanolamine are employed, e.g. to remove old paint and rust from bilges for cleaning and repainting same. Solutions of different citric acid and triethanolamine concentrations are employed, some having a relatively high concentration of these chemical agents, e.g. 10% citric acid and 5% triethanolamine, by weight, and some being more dilute, e.g. containing 5% citric acid and 2% triethanolamine. Also, final rinse solutions can be employed, e.g. containing only citric acid or only triethanolamine.
The wastewater produced in these operations contains in addition to citric acid and/or triethanolamine, heavy metal ions sludge, and oil and grease. Existing industrial waste treatment plants (IWTP) cannot treat effectively such wastewater to remove heavy metal ions and destroy citric acid and triethanolamine, since these chemical agents will chelate without being precipitated out, and the heavy metals or metal ions in the wastewater are generally considered toxic, and hence wastewater containing such materials cannot be sewered. Thus, for example, citric acid and triethanolamine-containing wastewater is simply diluted and hauled away for land disposal. However, the naval shipyards as the producers of the hazardous wastewater are liable for its final safe disposal.
Also, currently, industrial wastewater treatment plants at naval shipyards treat very dilute wastewaters containing only about 1% citric acid and 1% triethanolamine with potassium permanganate but this process produces considerable heat, requiring treatment of the wastewater over an extended period of time, e.g. 3 or 4 days, and results in the generation of an undesirable brown manganese dioxide precipitate in the sludge, and is a high cost operation. Concentrated wastewater containing about 10% citric acid and about 5% triethanolamine cannot be treated in this manner and must be disposed of by contractor hauling.
Ultraviolet light and hydrogen peroxide (H.sub.2 O.sub.2) techniques have been used heretofore to destroy hazardous organic chemicals such as benzene, trichloroethylene, dichloromethane and other halogenated aliphatics. However, such method is known to be generally effective on such organic compounds present in solution only in very low concentrations substantially below 1%, usually in the range of several hundred mg/l (ppm).
One object of the present invention is the destruction of citric acid and/or triethanolamine from wastewater, particularly wastewater employed in ship bilge cleaning operations, so that the toxic heavy metals also present will no longer form chelated compounds and subsequently can be removed from the watewater in IWTP by conventional precipitation procedure by adjusting the pH within a suitable range.
Another object is to treat the above citric acid and/or triethanolamine containing wastewater in a manner so as to decompose such materials into innocuous forms.
Still another object is to decompose substantially all of the citric acid and triethanolamine in wastewater containing relatively high concentrations of such materials, in an efficient cost effective process.